The present invention relates to apparatus for observing, locating and identifying features of interest in an observed field of view such as might be used, for example, in observing, locating and identifying stars or stellar constellations in an observed portion of the night sky.
Amateur astronomers interested in observing a stellar constellation or other feature in the night sky commonly use star charts to determine where to look to find the desired constellation or to identify what they are looking at. Such star charts give pictorial representations of stars and stellar constellations and sometimes indicate celestial coordinates by which the stars may be located. The amateur astronomer typically looks for the pattern of the constellation amongst the many stars in the sky, or if a single star, galaxy or other small feature is sought, the observer looks for the closest identifiable constellation and attempts to locate the desired feature within the pattern of the constellation. Alternatively, the observer may translate the coordinates of a desired feature from a star chart into compass bearing and elevation and then using a compass look in that direction. This approach has the disadvantages that it requires a degree of sophistication to know how to read a star chart, and it is difficult for most observers to aim a telescope, binoculars or the un-aided eye in a precise three-dimensional direction. The observer usually has to refer back and forth from the sky to the star chart. Separate illumination is usually needed to read the star chart in the field, and this presents a problem of the user's eye having to adjust to the vastly differing light levels of the night sky and the illuminated chart. In addition, a very limited amount of information may displayed on the star chart without making the chart unduly difficult to read.